Place a squash half, cut side down, in a large, microwavable dish. Add 1/2 cup water and microwave until tender, 10 to 15 minutes. Repeat with the remaining squash half. Discard the seeds. Using a fork, comb the squash into strands into a bowl. Toss with the parmesan and season with black pepper.

Meanwhile, in a large skillet, heat the olive oil over medium-high heat. Add the sausage and cook until no longer pink, about 6 minutes. Add the spinach and crushed red pepper and cook until wilted, about 2 minutes; season with salt and black pepper. Serve on top of the squash.